Motor-control system.



P. H. THOMAS.

MOTOR CONTROL SYSTEM.

APPLICATION FILED SEPT. 4, 1903.

945,008. Patented Dec. 28, 1909.

switch.

UNITED STATES PATENT OFFICE.

PERCY H. THOMAS, OF PITTSBUBG, PENNSYLVANIA, ASSIGNOR TO COOPEB HEWITTELECTRIC COMPANY, A CORPORATION OF NEW YORK.

MOTOR-CONTROL SYSTEM.

Specification of Letters Patent.

Application filed September 4, 1903.

945,008. Patented Dec. 28, 1909.

Serial No. 171,882.

To all 107mm it may concern:

Be it known that I, PERCY H. THOMAS, a citizen of the United States, andresident of I Pittsburg, county of Allegheny, State of Pennsylvania,have invented certain new and useful Improvements in Motor-ControlSystems, of which the following is a specificat1on.

The object of this invention is to provide economical and simple meansfor gradually accelerating a direct current motor which is supplied withpower from an alternating currentsource. As is well known, it ispossible to obtain gradual acceleration in such motorsby the use ofgroups or steps of series resistances. This method is, however,uneconomical and requires resistances of considerable bulk. \Vhen thismode of acceleration is employed, the energy consumed by the resistancesrepresents a cutting down of the total energy of the circuit andconsequently stands for a practical waste of energy inasmuch as theresistances contribute nothing to the active operation of the system.Under the operation of the invention disclosed herein, this waste isavoided. Practically the total energy of the circuit at any given timeis applied to the operation of'the motor, and the desired accelerationof the motor is accomplished by applying to it successively larger andlarger amounts of elec-. trical energy, none of which is wasted.

In carrying out my invention, I make use, among other things, of aso-called vapor converter adapted to transformalternating into'directcurrents. Incidentally the vapor converter employed may be provided withone or more additional or supplementary positive electrodes. I supply tothe motor a gradually varying direct current potential rom analternating source, preferably from The secondary of the transformer isshown at 2 as havin taps 3, 4, 5, 6 and 7, connected, respectively, toswitch terminals 8, 9, 10, 11 and 12. From one extremity of thetransformer a wire 13 leads to one side of the work circuit including adirect current motor 14. The other side, 15, of the work circuit isvapor converter, 17, the said converter being provided with two positiveelectrodes, 18 and 19. The electrode 18 is connected by a conductor, 20,with a switch terminal, 21, and the electrode 19 is connected by a.conductor, 22, with a switch terminal, 23.

The terminals 21 and 23 are adapted to cooperate with the describedterminals 8, 9, 10, 11 and 12, any suitable device being providedwhereby relative movement between these sets of terminals can beobtained. It should, however, be stated that the terminal devicesreferred to are so proportioned that during their relative movement theterminal 23, for example, will make contact with the terminal 11 beforethe terminal 21 leaves the terminal 12, and also that the terminal 21will make contact with the terminal 11 before the terminal 23 leaves thesame. This same relation holds with respect to the members of anysuccessive pair int-he'group of terminals 8, 9, 10, 11 and 12.

Across the terminals of the main transformer a circuit, 24, is placed,the same including the primary, 25, of a transformer, the secondary, 26,of which is connected to auxiliary positive electrodes, 27 and 28,inside the vapor converter 17. At an intermediate point in the secondary26 a conof the converter. In the conductor 29 Imay include a choke coil,30, the function of which is to store electrical energy during aintermediate oints of a transformer, the rise of potential in the'circuit and to disarrangementeing such that during succhar e a portionof the stored energy dur ng 'cessive periods of operation successively afal o potentlal, whereby the negatlve electrode 16 is maintained at alltimes in. an operative condition.

,The operation of the system thus far described is as follows: Thedirect current motor 14 is started from rest by so operating the switchterminals 21 and 23 that the terminal 23 makes contact with the terminal12, which is the lowest volta e tap provided from the secondary 2 oftfie main trans- ,former. This applies the alternations from thistransformer m a given direction to the higher and higher potentials areapplied to the motor through the action of a suitable I have illustratedmy invention in the accompanying drawings, in which- Figures 1 and 2 arediagrams of circuits and apparatus adapted to carry out my in- ,vention.I I

In the drawings, '1 is the rimary of a suitable transformer supplied roman alternating current source.

ductor, 29, leads. to .the negative electrode 16 connected to thenegative electrode, 16, of a motor 14, these accumulations of electricalenergy being supplied at the lowest voltage attainable from theapparatus. To accelerate the motor, the switch terminals 21 and 23-aremoved upward, the terminal 21 making contact with the terminal 12 beforethe terminal 23 leaves the terminal 12, thus running both positiveelectrodes 18 and 19 in parallel upon the tap 7. As the switch terminalsmove farther, the terminal 23 leaves the tap 7 leaving the terminal 18to carry the current, A moment later, the terminal 23 makes contact withthe terminal 11 of the tap 6, which is the tap on the next highervoltage, when the positive electrode 19 immediately supplies current tothe direct current motor 14 at the voltage of the tap 6. The positiveelectrode 18, though still connected to the tap 7, no longer suppliescurrent to the motor 14, since the tendency is for current to flow fromthe electrode 19 to the electrode 18. No current actually flows,however, into the electrode 18 in view of the initial reluctancecharacteristic of an electrode which tends to act as a negative. As theswitch terminals advance, the ter: minal 21 leaves-the terminal 12 andmakes contact with the terminal 11 before the terminal 23 leaves theterminal 11, the two electrodes 18 and 19 thus acting in parallel tosupply current to the motor 14. The cycle of operations just describedare then repeated between the taps 6 and 5, 5 and 4 and so on untilfinally the desired acceleration is attained in the motor and the latteris effected, if the conditions require, by the terminal voltage of thetransformer. If it is desired to lessen the speed of the motor or tosupply it with energy in lesser amount, the switch elements ma be madeto traverse the movements described in.the reverse direction in whichall the intermediate points of voltage will be applied to the motor alsoin a reverse direction. It must be noted, however, that in this case,since the positive electrode within the vapor converter which has thehigher potential tends to supply current, that it will be necessary forthe switch terminal 23 to break the circuit every time it leaves a tapterminal. However, since the terminal 18 is always ready to supply theener y to the motor at a slightly lower potentia a comparatively simplecircuit breaking device will suflice on the switch terminal 23. I amaware that a similar result has been obtained in some cases by the useof a sliding contact passing from tap to tap and broad enough to bridgetwo successive taps. Such a switching device is provided with animpedance coil to reduce the current which necessarily results from theshort circuiting of a ortion of the secondary of the supply transfbrmer.In the device described in Fig. 1, no contact bridges two taps from thetransformer and no short circuit current can flow, since neitherpositive electrode 18 or 19 can act as a negative.

In case the motor is used for propelling vehicles or similar service inwhich no gradual decrease in speed is required, it is desirable when themotor, running upon the maximum voltage, is to be stopped to open thesupply circuit by any suitable circuit breaker, or where the characterof the vapor device is suitable, by opening the circuit of the auxiliarytransformer 25, 26 at any suitable point.

The organization illustrated in Fig. 1 is adapted to supply to themotor, current of one direction, by utilizing every other alternation ofthe supply circuit. In Fig.2, however, the corresponding motor isaffected by current of one direction in which both phases of the supplycurrent are utilized. In this second figure of the drawing, the vaporconverter is supplied with three main positive electrodes, 31, 32 and33, connected respectively to contact terminals 34, 35 and 36. The saidterminals are adapted to cooperate with other switch terminals having arelative movement as regards the first named terminals, the group ofcooperating terminals being shown at 37, 38, 39, 40, 41 and 42. Each ofthese terminals is connected by a tap with a loop of the transformersecondary 2, or else with a terminal of the said secondary. In thedrawing the terminals 37 and 39 are connected to opposite terminals ofthe secondary.

The operation of accelerating the motor 14 in Fig. 2 is the same inprinciple as that already described in connection with Fig. 1. To startthe motor from rest, the switch terminals 34, 35 and 36 move into thefirst position in which they connect with the contacts 38 and 42, 36engaging .with 38, and 34 and 35 with 42. The result is the connectionelectrically of the positive terminal 33 with the lowest voltage tap onone side of the transformer secondary 2 and the positive electrodes 31and 32 to the corresponding tap on the other side of the secondary 2, sothat the lowest voltage impulses attainable are appliedto the motor 14."To accelerate the motor 14 further the switch terminals 34, 35, and 36make contact with the stationary terminals 41, 42 and 38, respectively.The positive electrode 33 is then supplied from-the same tap as above.The positive electrode 31 is supplied from the next higher tap from theother side of the secondary 2 and though the positive electrode 32 isconnected with the stationary switch terminal 42, it supplies nocurrent, as the positive electrode 31 has a higher voltage. For the nextstep, the switch terminals 34, 35 and 36 are in contact respectively.with stationary terminals 41, 40 and 38 the result being that thepositive electrode 32 is supplied from the second tap on one side of thesecondary 2 and the positive electrode 31 from the corresponding tap onthe other side of the secondary 2. The positive electrode 33, thoughconnected to t e stationary terminal 38, supplies no current for reasonsalready explained. By exactly similar steps the voltage appliedto themotor 14 is increased step by step until, if desired, the full terminalvoltage of the transformer secondary 2 is applied on both sides to thevapor converter 17.

I The statements made in. the description of Fig. 1, regarding thereduction of speed of the motor either by proceeding over the stepsdescribed in the reverse order or by opening the circuit entirely, applywith equal force to Fig. 2. It is evidently possible, where both sidesof a transformer are used to supply all alternations from the source tothe motor, that two additional positive electrodes may be used, in whichcase both sides of the transformer may be stepped up or down at the sametime.

The principles described in connection with this invention areapplicable to other processes than the acceleration of direct .currentmotors. Any direct current work requiring a variation of potential maymake use of this principle and wherever it is convenient and desirableto stop flow of current in a positive electrode by the application of ahigher potential either from the, same source or other source, this canreadily be done by the means of an additional positive terminal abovedescribed.

In a divisional application filed by me De- December 4, 1903, SerialNumber 183,097,

claims are made upon the apparatus described herein. In anotherdivisional ap lication, filed by me November 30th, 1909, erial Number530,528 other features of the apparatus described herein relating moreparticularly to the means for smoothly step ing up the voltage and thearrangement 0 the keeping alive apparatus, are claimed.

I claim as my invention:

1. In a system of electrical distribution in which suitable directcurrent translating devices are supplied with variable direct voltagefrom an alternating source, the method of control which consists insupplying current from the source from a definite potential andrectifying this current, and, increasing the voltage supplied to thetranslating devices, by substituting for this rectified current, currentfrom a point of higher potential from the source and independentlyrectifying the second current.

2. The method of increasing the volta e supplied from an alternatingsource to a irect current translating device, which conhigher voltagesto the device through a plurality of paths, closing the path from ahigher voltage before opening the path from the lower voltage, andrectifying the current in each path independently.

Signed at New York, in the county of New York, and State of New York,this 1st day of September, A. D. 1903.

PERCY H. THOMAS.

Witnesses:

WM. H. GAPEL,

THos. H. BROWN.

sists in applying successively higher and.

